This application is entitled to the benefit of, claims priority from, and incorporates by reference subject matter disclosed in German Patent Application No. 10048816.1, filed on Sep. 29, 2000.
The invention relates to a pressure regulating valve for a refrigerating plant, having a slider member that can be moved relative to a guide by means of a drive device, with variable throttle resistance being created between the guide and slider member.
Such pressure regulating valves are generally used in a refrigerant circuit between an evaporator and a compressor, wherein the refrigerant circuit comprises a condenser connected to the compressor, in which condenser the refrigerant is liquefied and which condenser is connected to the inlet of the evaporator by way of an expansion valve. In such a refrigerant circuit, the pressure regulating valve regulates the pressure in the evaporator and thus regulates the temperature of evaporation. It is thus possible for the evaporation pressure to be regulated largely independently of the suction pressure of the compressor, provided that the pressure in the evaporator is higher than the suction pressure. This enables very precise regulation of the temperature in the regions that are to be cooled by means of the evaporator. By means of such electronic control of the valve it is possible to keep the temperature ranges in those regions constant to within xc2x10.1xc2x0 C. Such precision places relatively high demands, however, on the pressure regulating valve. In particular, it must be capable of regulating very accurately relatively small and relatively large refrigerant flows.
Such a pressure regulating valve can regulate the suction pressure of the compressor in the refrigerant circuit also when the refrigerating plant is starting up. In that case, regulation is effected with reference to pressure measurements at the suction side of the compressor. It is thus possible to protect the compressor against overloading as the device is started up.
EP 0 741 257 B1 discloses a valve in a refrigerant circuit, but in that case it is an expansion valve. That expansion valve has a slider member that engages round a guide in the manner of a sleeve. The guide is in the form of a hollow cylinder that has one or more openings in its wall, which openings are covered up to a greater or lesser extent by the slider member. The slider member is driven by an electronically controlled stepper motor.
U.S. Pat. No. 5,964,248 describes a valve intended for regulating superheated vapour. That valve has a relatively large regulating range, that is to say it can control very large amounts of vapour as well as very small amounts of vapour. For that purpose, the slider member is displaceable in a hollow cylindrically shaped guide that has in its wall a number of holes arranged above one another in the direction of movement of the slider member, which holes are exposed gradually as the slider member moves. At its closure end, the slider member has an apron, in the wall of which likewise holes are arranged, so that as the apron moves away from a valve seat initially those holes are exposed and allow vapour to flow through. The manufacture of such a valve is extremely expensive because of all the holes. The parts that are moved relative to one another have to be manufactured with relatively high precision to ensure that the valve remains leakproof.
The problem underlying the invention is to be able to control refrigerant over a large throughput range by means of a valve that can be manufactured inexpensively.
The problem is solved in a pressure regulating valve of the type mentioned at the beginning in that the slider member and the guide co-operate in two sections of their movement relative to one another according to different valve principles.
In that construction, for one section of movement a valve principle can be selected by means of which large amounts of gaseous refrigerant can be regulated or controlled. That valve principle is based essentially on the fact that the surface area of passage is large and the throttling as a result of the co-operation of the slider member and guide is relatively small. A different valve principle can be used for the other regulating region, however, which is based on regulating as small amounts of refrigerant vapour as possible. For small amounts, a correspondingly larger throttle resistance is required. As a result of using two different valve principles, both requirements can now be combined without difficulty.
It is preferred for the slider member and the guide to create a flow resistance that is determined, in a first section of movement, by altering the covering of an opening in one of the two parts, slider member and guide, and, in a second section of movement, by altering the size of a gap between the slider member and guide. In the first section of movement, the valve operates, so to speak, according to the principle of a xe2x80x9cneedle valvexe2x80x9d, whereas in the second section it operates according to the xe2x80x9ccage valve principlexe2x80x9d. By covering an opening, or exposing it partially or completely, a flow path for the gaseous refrigerant can be set that enables a relatively large volume flow of the refrigerant. A window, so to speak, is being opened and closed. In the other section of movement, however, it is possible to operate with much more precision by controlling the gap. The same displacement of the slider member relative to the guide then results in a much smaller change in the flow resistance.
It is preferred for the two sections of movement to be contiguous with one another. That has the advantage that the transition from one valve principle, for example from the cage valve principle, to the other valve principle, in the present case the needle valve principle, can occur gradually so to speak. That transition can be taken into account in the regulation.
Preferably the slider member and the guide rest against one another with their end faces in the closed state. This enables the valve to close completely with high reliability. It is less expensive to make end-face contact completely leakproof than to make a seal around the circumference completely leakproof.
Preferably the end-face contact is achieved by the co-operation of a circumferential virtually line-contact end-face sealing edge and a yielding sealing face into which the sealing edge can be pressed. Only relatively small forces are thus required to render the valve leakproof in the closed state, since even relatively small forces effect a relatively large surface pressure on the contact region between the sealing edge and the sealing face, which is what ultimately brings about sealing.
Preferably the drive device can be controlled incrementally and the sealing face is sufficiently yielding for the sealing edge to be able to penetrate by the length of at least one increment. An incrementally controllable drive device is provided, for example, by a stepper motor. Such a stepper motor can only ever adopt predetermined positions which, optionally taking transmission into account, result in stepwise movement of the slider member relative to the guide. It can also happen that the slider member and the guide have not quite come into contact with one another in one position of the stepper motor but the next position of the stepper motor can only be reached if the sealing edge can penetrate into the sealing face. If instead the sealing face is sufficiently yielding to enable penetration of the sealing edge by the length of at least one increment, then it is not necessary to ensure that the stepper motor stops precisely where the sealing edge rests against the sealing face. It is preferred to use a flexible material for the sealing face, for example an elastomer.
Preferably the slider member tapers conically from its contact face towards the head. With that construction it is possible to achieve a valve function based on the needle valve principle. When the slider member moves relative to the guide, a gap between the guide and the slider member becomes larger or smaller as a result of the conical shape of the slider member, which co-operates with an edge of the guide. The angle of incline of the conically widened portion determines the opening, that is to say the change in the size of the gap in relation to the displacement of the slider member relative to the guide.
Preferably the slider member is in the form of a beaker-like hollow cylinder having an open end face, which slider member is held in an auxiliary guide at a distance from the guide. The load on the guide is thus kept small. Since the guide is arranged spaced from the auxiliary guide, the slider member is held at two regions that are relatively far apart from one another in the direction of movement. The risk of the slider member tilting relative to the guide and thus of an undesirable skewed position arising is kept small.
Preferably the slider member has an opening in its circumferential wall between its closed end face and the conically widened portion. That opening is blocked off to a greater or lesser extent by the guide upon movement of the slider member and guide relative to one another. When the slider member is moved further relative to the guide so that the conically widened portion co-operates with the guide, then a transition occurs between the cage valve function and the needle valve function.
Preferably an inlet in a housing is connected to the open end face and an outlet branches off from the housing between the guide and the auxiliary guide. The auxiliary guide can then assume an additional role, which is to seal off the inlet and outlet from one another. The xe2x80x9ccontrol edgexe2x80x9d of the guide is then arranged at the end of the guide facing the auxiliary guide. The outlet is thus connected, so to speak, to a xe2x80x9ccontrol chamberxe2x80x9d formed between the guide and the auxiliary guide on the outside of the slider member.
Preferably the auxiliary guide is held in the housing by force fit or interlocking fit. This facilitates manufacture. It is not necessary to secure the auxiliary guide in the housing by soldering, welding or adhesion. Instead, it is sufficient to join the auxiliary guide to the housing, for example, by a bead or by other deformation of the housing.
Preferably the drive device has a spindle drive that co-operates with an end wall of the slider member and the slider member is secured against rotation in the guide. The guide thus assumes a further role. It prevents the slider member from rotating, so enabling displacement of the slider member relative to the guide by rotation of a spindle, which is driven, for example, by a stepper motor. The spindle thus enables a relatively large transmission factor so that the position of the slider member relative to the guide can be controlled with high precision.
Preferably a pressure compensation path is provided, which spans an area of contact between the slider member and guide. It is thus possible for the slider member to be loaded on both its sides in the direction of movement by the same refrigerant pressure. This in turn lessens the load on the drive device of the slider member so that stepper motors can be used, which are themselves not capable of delivering a relatively large force.
Preferably the guide forms a seat for the drive device, so providing a defined position of the drive device relative to the slider member.